Abstract
In this study, the fatigue behaviour of friction stir welded (FSW) joints of AZ61 magnesium alloy was investigated. AZ61 plates were joined with a welding speed of 100 mm/min and a tool rotational speed of 1200 rpm. The microstructure of the weld zone was classified into three regions: stir zone (SZ), thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). In the SZ, fine equiaxed grains resulting from dynamic recrystallization were observed, where Vickers hardness was higher than in the parent metal. Fatigue tests were conducted under fully reversed axial loading (R = -1). The fatigue strength of FSW joints was higher than that of the parent metal, which could be attributed to the fine grain structure in the weld zone. Fatigue crack initiated at the boundary between SZ and TMAZ on the advancing side of the bottom plane. Such predominant crack initiation at the boundary was due to the texture developed during the welding process.
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